The son of a Chinese immigrant family, Mah was born in Bashaw, Alberta in 1926.^[1][4] English was his native language and he did not speak Mandarin, but he was able to write his Chinese name.^[4] He earned an arts degree from the University of Alberta in 1952, a physical education degree from McMaster University in 1960, a Bachelor of Education from the University of Toronto in 1962, and a master's degree in education from the University of Toronto around 1970.^[1] Mah taught in Ontario from 1955 to 1970.^[1] From 1970 to 1988, he also established and taught exercise and cardiac rehabilitation classes at the University of Toledo where he was a physical education instructor.^[1][5][6]

Mah joined the Chinese Association of Greater Toledo in 1970 and later served as its program director.^[4]

Mah, described as "an ordinary runner of ordinary speed", did not begin running marathons until he was 40.^[1][2] He reportedly took up the sport to prevent heart disease that ran in his family.^[6] In 1964, he formed the Metro Toronto Fitness Club with three others, and later started the North York Track Club where he coached Maureen Wilton.^[1][7][8] That club was considered one of the best in North America and Wilton was one of its star athletes.^[8]

Mah and the 13-year-old Wilton both ran their debut marathons on May 6, 1967, at York University in Toronto, Ontario.^[8][9] Wilton ran the first three laps of the five lap course with Mah and she went on to finish in a time of 3:15:23, a performance recognized as a world best by the International Association of Athletics Federations.^{[8][9][nb 2]} Invited by Mah, Kathrine Switzer also ran that day – only sixteen days after her historic run at the Boston Marathon.^[8]

Mah ran the Glass City Marathon in Toledo, Ohio numerous times, his first at the inaugural event in 1971.^[13] By 1977, he completed his 100th marathon there with a 3:18:18 performance.^[13] Three years at the same race, his tenth on the Glass City course, Mah posted his 173rd.^[13] In 1981, Mah ran his 198th marathon to break the record for most marathons set by Ted Corbitt.^[1] When possible, race directors would issue bib numbers to match his marathon total.^[1] He would later run his 300th in Detroit (1983), his 400th in Virginia (1986), and his 500th in Boston (1988).^[1] The 1984 New York City Marathon was Mah's 348th marathon and 35th of the year.^[14] At least one race director scheduled back-to-back marathons on Saturday and Sunday to help him add to his totals.^[15] Mah ran the Boston Marathon twenty times and was a regular participant in ultramarathons and triathlons as well as cross-country skiing and canoe races.^[1][2]

In recognition of his role in promoting the sport of distance running, he was invited to participate in the 152-mile Spartathlon in Greece.^[16] Although he did not finish the event, he was publicly honored by the Greeks for "his love of competition".^[16] Mah's personal best over the marathon distance was 3:13, however, he felt he could go faster if determined to do so.^[1] Hal Higdon commented that he believed Mah was capable of running a marathon under three hours if he trained for a specific race.^[17]

Mah's last race was a 50 kilometer event Labour Day weekend, 1988, in St. Jacobs, Ontario; he dropped out of the Toronto Marathon three weeks later.^[1] Mah's record would last until 1994 when broken by Norm Frank of Rochester, New York.^{[17][nb 3]}

Following a lingering bout of hepatitis, Mah died of leukemia at the St. Vincent Mercy Medical Center in Toledo, Ohio in 1988.^[1] Following his death, he was a subject of a case report that appeared in the May 1991 issue of the medical journal Chest.^[2] According to that report, Mah received a cardiac stress test nine months prior to his death which found "ischemia with disseminated circadian variation suggesting possible [coronary vasospasm] without angina."^[2] Autopsy revealed localized fibrosis of the left papillary muscles, but no evidence of coronary atherosclerosis.^[2]

Mah has been described as "an early leader of the modern running boom".^[18] Joe Henderson wrote an editorial in tribute to Mah in 1989.^[19] According to Henderson, Mah stated: "I believe Americans have been brainwashed with the idea that they must do less because increased age will result in less energy and diminished capacity. I have found this is simply not true if a person does not allow his mind to accept the traditional view of aging."^[19]

Along with Dick Beardsley, Herb Lorenz, and Harold Tinsley, Mah was a 1989 inductee of the Road Runners Club of America's Hall of Fame.^[20]

The Sy Mah Memorial Scholarship at the University of Toledo was established in 1990 by Mah's friend and family.^[3] In addition to meeting various academic standards, qualified recipients within the College of Health Science and Human Service are required to be "avid social runners".^[3] A portion of the proceeds from the annual Glass City Marathon go to fund this award.^[6] Participants in that race pass by a life-size statue of Mah that was dedicated September 13, 2002 in Olander Park in Sylvania, Ohio.^[6][21] The statue was created by Thomas Lingeman, a Professor of Art at the University of Toledo, who was commissioned by the Toledo Road Runners Club.^[5]

At the annual Sri Chinmoy 24-Hour Race in Ottawa, Ontario, Canada, the Sy Mah Award is given to the runner who completes at least 100 miles and runs the most even 50-mile splits.^[22] The wood-carved trophy is shaped to resemble an hourglass symbolizing Mah's "balance and steadiness".^[23]

Mah's papers are held at the Ward M. Canaday Center at the University of Toledo.